Myocardial ischemia is often detected by the application of cardiac stress, for example, stress caused by exercise or pharmaceutical injection. In general, ischemia conditions can be detected by changes in the ECG signals or by techniques of cardiac imaging.
One type of ECG analysis includes analyzing high frequency components in a QRS complex of a heart beat. One of the indications for ischemia is a reduction in the intensity of a high frequency band in the QRS complex. For example, Beker et al (“Analysis of High Frequency QRS Potential during Exercise Testing Patients with Coronary Artery Disease and in Healthy Subjects”, Biomedical Engineering Department, Faculty of Engineering, Tel-Aviv University, 1995), Abboud et al (Analysis of High Frequency Mid-QRS Potentials vs ST segment and T Wave Analysis for the Diagnosis of Ischemic Heart Disease, IEEE Computers in Cardiology 2003; 30:813-814), Sharir et al (Detection of Stress-Induced Myocardial Ischemia using Analysis of High-Frequency QRS Components. Journal of the American College of Cardiology 2006: 47 (4), 132A), the disclosures of which are hereby incorporated herein by reference, discuss analyzing a high frequency signal of the QRS complex during an exercise test.
US patent applications 20030013978 by Schlegel et al. and 20040039292 by Schlegel et al. and Rahman et al (High-frequency QRS electrocardiogram predicts perfusion defects during myocardial perfusion imaging, Journal of Electrocardiology 2006:39; 73-81) disclose RAZ analysis of the high frequency waveform.
U.S. Pat. No. 7,151,957 to Beker et al., the contents of which are hereby incorporated by reference, discloses methods of high frequency waveform averaging to obtain an improved signal to noise ratio from such a signal.
Simpson, in U.S. Pat. No. 4,422,459, teaches a system which analyzes only the late portion of the QRS interval and early portion of the ST segment, and in an off-line fashion. Albert et al., U.S. Pat. No. 5,117,833, partially focuses on analyzing signals within the mid-portion of the QRS interval for the indication of cardiac abnormality. Albert et al., U.S. Pat. No. 5,046,504, similarly teaches the acquisition of QRS data and subsequent analysis. Seegobin, in U.S. Pat. Nos. 5,655,540 and 5,954,664, provides a method for identifying coronary artery disease. Hutson, U.S. Pat. No. 5,348,020, teaches a technique of near real-time analysis and display. Beker, in patent application WO2005/104937, teaches a technique for analysis of high frequency QRS complexes. Pettersson et al (Changes in high-frequency QRS components are more sensitive than ST-segment deviation for detecting acute coronary artery occlusion. Journal of the American College of Cardiology 2000; 36:1827-34) analyzed changes in HF-QRS in patients undergoing coronary angioplasty.
U.S. Pat. No. 7,113,820 to Schlegel et al., the disclosure of which is incorporated by reference, shows a detection of a reduced amplitude zone (RAZ) within the high frequency waveform of ECG signals.